In modern communication technology, digital data form a data stream which is to be fed by a data source to a data receiver. This data stream is generally fed via electrical or optical lines. When transmitted through these lines, the data stream is exposed to external interference effects. These interference effects can corrupt the individual data (bits) in the data stream stochastically or deterministically. As a result, the received data stream is encumbered with corresponding stochastic or deterministic bit errors.
Modern transmission systems often have an intermediate path, by which the data stream, coming from a data source, is supplied to a transmission path. For data protection, before entering into the transmission path, the data stream is scrambled in a scrambler following the intermediate path in accordance with a specified instruction by a known period length and, after emerging from the transmission path, descrambled by a descrambler in accordance with the specified instruction. Moreover, the successive occurrence of a plurality of direct data is thus avoided in the data stream. Such a successive occurrence would otherwise result in the data stream to be transmitted having a large same component. It would also be reflected in the transmission quality when system components (such as amplifiers) are used in the line for transmitting data, due to their relatively unfavorable transmission performance characteristics for same components.
In principle, the way the scrambling, or rather descrambling, operations are carried out is that bit errors occurring after the scrambling operation are multiplied by a previously known period length, and the bit errors occurring before the scrambling operation are contained as unmultiplied bit errors in the descrambled data stream that emerges from the transmission path.
The European Patent, EP-A2-0 094 902 discloses a method for localizing the origin of bit errors in a data stream, which, coming from a data stream, arrives via a transmission path consisting of a plurality of path sections at a data receiver. Each path section is delimited on the input side by a scrambler and, on the output side, by a descrambler. The scrambler and descrambler of a path section each have circuit elements (scrambling instructions) specific to a path section, so that bit errors occurring in one path section undergo a descrambler-specific multiplication. Deviations established from a comparison of transmitted test data to received test data are registered and, in some instances, automatically evaluated in a manner that is not described in greater detail. A relatively high level of complexity is required to evaluate the various descrambler-specific bit-error patterns. The European Patent, EP-A2-0 094 902 does not mention locating errors in an intermediate path, through which the data stream arrives in a state in which it has not been scrambled.
Thus, there exists a need to devise a process for determining the origin of bit errors in a data stream, which arrives in a state in which it has not been scrambled via at least one intermediate path and, in a scrambled state, arrives via at least one transmission path at a data receiver, the process being distinguished by a low level of complexity for implementation and evaluation and which, nevertheless, permits the origin of bit errors to be determined accurately and simply.